1. Field of the Invention
The invention relates in general to a filter, and more particularly to a filter enabling the pulse width of the input signal to be the same with that of the output signal without using an additional set of high frequency pulse.
2. Description of the Related Art
Many digital signal interfaces and universal serial buses (USB) have a specification regarding minimum pulse width and noise suppression to avoid the noise of an electronic system affecting the quality of digital signal and incurring erroneous actions. In prior art, such problem is resolved by using a first conventional filter or a second conventional filter.
First Conventional Filter:
Referring to FIG. 1, a first conventional filter is shown. The first conventional filter 10 includes an inverter 110, a resistor R and a capacitor C. The inverter 110 inverts the input signal Sin1 to an inverse input signal Sin1′. The inverse input signal Sin1′ is filtered by the resistor R and the capacitor C and then outputted as an output signal Sout1.
However, the conventional filter 10 makes the overall signals decayed. As a result, the pulse width of the output signal Sout1 cannot maintain the same with that of the input signal Sin1.
Second Conventional Filter:
FIG. 2 of the US Patent No. US2007/0071085 discloses another conventional filter which filters the noise by receiving an additional set of high frequency pulse.
Currently, the electronic system is directed towards low power consumption, and most of the time, an electronic system would work on a stand-by mode or a sleep mode. An electronic system working on a stand-by mode or a sleep mode cannot provide high frequency pulse to the conventional filter to filter the noise.